Will gelcoat fill pinholes?

Discussion in 'Materials' started by Nick Shaw, Oct 20, 2023.

  1. Nick Shaw
    Joined: Oct 2023
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    Location: North Saanich, BC

    Nick Shaw Junior Member

    After sanding LBI 940 vinylester fairing compound there are a lot of small pinholes. I plan to apply gelcoat over this. Will the gelcoat fill in the pinholes? I don’t want the, “bridges over”. Should I fill them with a low viscosity filler? What’s the best filler for this purpose?
    Thanks
     
  2. ondarvr
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    ondarvr Senior Member

    It all depends on what you mean by pin holes. Typically pin holes will be bridged over for the most part if they're small.

    You can squeegee gel coat over the surface and force it into the pits right before spraying. This works, but becomes a little more difficult as you scale up in size.
     
  3. Nick Shaw
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    Nick Shaw Junior Member

    The pin holes are maybe 0.5mm diameter. Do you think it’s good just to use the squeegeed gel coat? … we’re planning on rolling on the gel coat since it’s below the water line and will get an epoxy barrier coat on top before antifouling. Or would it be better to use some other low viscosity fairing compound also squeegeed on prior to gel coat?
    In spite of reading otherwise Im a little concerned about using an epoxy product then gelcoat. Am I being paranoid…..many posts seem to say gelcoat adheres to epoxy just fine.
    You may ask why gelcoat at all…it was planned to use vinyl ester gel coat followed by epoxy barrier as a “belt and suspenders” effort to be more water proof.
    Thanks
    Comments?
     
  4. Nick Shaw
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    Nick Shaw Junior Member

    I should add that the guys doing this job for me are complaining the LBI fairing compound is too hard to sand. I can empathize but it was the product they recommend.
     
  5. ondarvr
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    ondarvr Senior Member

    There is no need for gel coat if you are going to use an epoxy barrier coat.
     
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  6. kapnD
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    kapnD Senior Member

    You’re still in the fairing/sanding phase, why not fill those pinholes now, before painting?
    That’s the kind of thing that shows up as blisters over time.
     
  7. Nick Shaw
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    Nick Shaw Junior Member

    That’s my thinking. Hence my question…. Will VE gelcoat fill them or should I use more of the same LBI 940 VE fairing compound? The guys doing the sanding are complaining it’s very hard to sand. Strange as the manufacturer claimed is sands easily. I’ll be phoning them (LB I) tomorrow morning to see what they recommend.
     
  8. ondarvr
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    ondarvr Senior Member

    Gel coat will typically be much harder to sand than any type of fairing compound.
     
  9. kapnD
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    kapnD Senior Member

    hmmm, that makes me wonder if your guys know what they’re doing?
    Are they using professional sanding tools with correct sandpaper?
    Fairing compound does get harder over time, I like to sand it as soon as practical after application.
    Hardware store sandpaper sucks!
     
  10. Nick Shaw
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    Nick Shaw Junior Member

    They’re supposed to be professionals but I’m seriously wondering
     
  11. ondarvr
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    ondarvr Senior Member

    Maybe we need to know a little bit more about the entire project because some of the information doesn't make sence.
     
  12. kitcarman
    Joined: Oct 2023
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    kitcarman New Member

    From my experience (which is limited to kit cars using polyester resins and gelcoats)...... filling gelcoat pinholes is very difficult and tedious. I've found the only way is to prepare the area by cleaning with acetone, and then drip some gelcoat onto the pinhole - this WILL NOT successfully fill the hole unless you do the following. Take a small implement eg a thin strip of timber (coffee stirrer?) sharpened to a point, and direct this through the liquid gelcoat into the pinhole and agitate it to ensure any trapped air is removed. A long and tedious process - maybe if you have the equipment car screen fitters use to 'vacuum' an area to introduce resin and repair cracks, that would be a way to make it easier to resolve.
     

  13. sharpiedory
    Joined: Oct 2023
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    Location: Maine

    sharpiedory Junior Member

    Pinholes are annoying.. worth taking the time to putty generally. With good technique a pinhole can be puttied leaving little to no extra to sand off.
     
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